Summary: The rate of intraoperative neuromonitoring events was 3.6% when utilizing both TcMEPs and SSEPs during AIS surgery. The majority (86%) of these returned to baseline following corrective action: elevate blood pressure, adjust screw position, and remove traction. Of the 3 that remained abnormal, 2 awoke with neurologic deficits
Introduction: The purpose of this study was to determine the frequency and outcome of intraoperative neuromonitoring alerts during surgical correction of AIS.
Methods: Prospectively gathered clinical data and intraoperative neuromonitoring reports recorded during spinal surgery for AIS were analyzed. Patients were divided into two groups, those with clear intra‐operative neuromonitoring changes and those with no intra‐operative neuromonitoring events. A neuromonitoring event was defined as a change from baseline Transcranial Motor Evoked Potentials (TcMEPs) or SomatoSensory Evoked Potentials (SSEPs) in the lower extremities. The risk, rate, cause and outcome of each neuromonitoring alert were assessed.
Results: A total of 582 AIS cases were analyzed. 21 cases (3.61%) had an intraoperative neuromonitoring event. In 18 of the 21 cases (86 %) the potentials returned to baseline following corrective action. Of the 3 with remaining abnormalities, 2 (0.3%) awoke with deficits (1 with unilateral weakness, 1 with unilateral sensory changes). In 12 cases the changes were thought to be due to low BP, all responded to elevation of the mean arterial pressure. 5 changes were associated with misplaced screws (in 4 the monitoring returned after removal/redirection, all 5 normal postop). Traction was the cause in 2 cases, both responding to reduction in traction. In 4 cases the cause was unclear. 2 remained abnormal and both awoke with a neuro deficit. There were no postoperative neurologic deficits in any cases with normal neuromonitoring. Surgical time (416 min vs. 290 min, p<0.001) and estimated blood loss (1971 ml vs. 1034 ml, p<0.001) were both significantly increased in the cases in which intraoperative events were observed.
Conclusion: The rate of neuromonitoring changes was 3.6% when utilizing both TcMEP and SSEP monitoring, most responsive to elevation of the MAP. When a cause was identified and corrective action taken, there were no postoperative neuro deficits. 2 of the 582 cases (0.3%) had postop deficits, both in cases where the cause of the change was unclear.